Update from the 26th of November 2021
And indeed it came. Magnetic storage is not dead but has instead become the solution for data hoarders, archival and write-intesive activities which could shorten the lifespan of SSDs. As for their performance and price, they never failed to impress year after year.
In 2016, good SSDs were priced between $250 and $300 per TB as stated in this article from then. A few months ago, I purchased a new 1TB SSD to speed up an old computer for just over $100 in a local computer parts shop. At the time of writing, it is not uncommon to find drives at $80 or less thanks to promo codes and special offers.
As for performance, moving from SATA to M.2 interfaces and using the full capacity of PCIe Gen 3 then PCIe Gen 4 certainly helped, as are improvements to the SSD controllers to avoid drops of performance after long read sequences. At the micro level, improvements to the cells, the actual transistors that store data, improved performance and storage density at the cost of the longevity of the drive.
Finally, the gaming industry and the fact that AMD has graphics cards and CPUs to offer brought us one final major improvement: DirectStorage APIs. Until now, game developers had to transfer graphical game assets from your storage to the CPU then to the CPU to the graphics card. This process uses processing power and wastes bandwidth: the CPU does not need to be in the middle there. That is exacty the value proposition: directly connecting storage and graphics cards to free up computing resources, bandwidth and improve latency. Performance will improve over time too with better hardware and interfaces, more capable communication protocols and APIs.